Le Gia Vinh’s Blog

RAID Level 0: Striped Disk Array without Fault Tolerance

 RAID Level 0 requires a minimum od 2 drives to implement

Characteristics & Advantages

• RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive
• I/O performance is greatly improved by spreading the I/O load across many channels and drives
• Best performance is achieved when data is striped across multiple controllers with only one drive per controller
• No parity calculation overhead is involved
• Very simple design
• Easy to implement

Disadvantages

• Not a “True” RAID because it is NOT fault-tolerant
• The failure of just one drive will result in all data in an array being lost
• Should never be used in mission critical environments

Recommended Applications

Video Production and Editing

Image Editing

Pre-Press Applications

Any application requiring high bandwidth

Raid Level 1: Mirroring & Duplexing

 

RAID Level 1 requires a minimum of 2 drives to implement

Characteristics & Advantages

• One Write or two Reads possible per mirrored pair							

• Twice the Read transaction rate of single disks, same Write transaction rate as single disks
• 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk
• Transfer rate per block is equal to that of a single disk
• Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures
• Simplest RAID storage subsystem design

Disadvantages

• Highest disk overhead of all RAID types (100%) - inefficient
• Typically the RAID function is done by system software, loading the CPU/Server and possibly degrading throughput at high activity levels. Hardware implementation is strongly recommended
• May not support hot swap of failed disk when implemented in “software”

Recommended Applications

Accounting

Payroll

Financial

Any application requiring very high availability

RAID Level 2: Hamming Code ECC

 

Each bit of data word is written to a data disk drive (4 in this example: 0 to 3). Each data word has its Hamming Code ECC word recorded on the ECC disks. On Read, the ECC code verifies correct data or corrects single disk errors.

Characteristics & Advantages

• “On the fly” data error correction
• Extremely high data transfer rates possible
• The higher the data transfer rate required, the better the ratio of data disks to ECC disks
• Relatively simple controller design compared to RAID levels 3,4 & 5

Disadvantages

• Very high ratio of ECC disks to data disks with smaller word sizes - inefficient
• Entry level cost very high - requires very high transfer rate requirement to justify
• Transaction rate is equal to that of a single disk at best (with spindle synchronization)
• No commercial implementations exist / not commercially viable

RAID Level 3: Parallel Transfer with Parity

 

The data block is subdivided (”striped”) and written on the data disks. Stripe parity is generated on Writes, recorded on the parity disk and checked on Reads. RAID Level 3 requires a minimum of 3 drives to implement

Characteristics & Advantages

• Very high Read data transfer rate
• Very high Write data transfer rate
• Disk failure has an insignificant impact on throughput
• Low ratio of ECC (Parity) disks to data disks means high efficiency

Disadvantages

• Transaction rate equal to that of a single disk drive at best (if spindles are synchronized)
• Controller design is fairly complex
• Very difficult and resource intensive to do as a “software” RAID

Recommended Applications

Video Production and live streaming

Image Editing

Video Editing

Prepress Applications

Any application requiring high throughput

RAID Level 4: Independent Data Disks with Shared Parity Disk

 

Each entire block is written onto a data disk. Parity for same rank blocks is generated on Writes, recorded on the parity disk and checked on Reads.

RAID Level 4 requires a minimum of 3 drives to implement

Characteristics & Advantages

• Very high Read data transaction rate
• Low ratio of ECC (Parity) disks to data disks means high efficiency
• High aggregate Read transfer rate

Disadvantages

• Quite complex controller design
• Worst Write transaction rate and Write aggregate transfer rate
• Difficult and inefficient data rebuild in the event of disk failure
• Block Read transfer rate equal to that of a single disk

RAID Level 5: Independent Data Disks with Distributed Parity Blocks

Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads. RAID Level 5 requires a minimum of 3 drives to implement

Characteristics & Advantages

• Highest Read data transaction rate
• Medium Write data transaction rate
• Low ratio of ECC (Parity) disks to data disks means high efficiency
• Good aggregate transfer rate

Disadvantages

• Disk failure has a medium impact on throughput
• Most complex controller design
• Difficult to rebuild in the event of a disk failure (as compared to RAID level 1)
• Individual block data transfer rate same as single disk

Recommended Applications

File and Application servers

Database servers

Web, E-mail, and News servers

Intranet servers

Most versatile RAID level

RAID Level 6: Independent Data Disks with Two Independent Distributed Parity Schemes

Two independent parity computations must be used in order to provide protection against double disk failure. Two different algorithms are employed to achieve this purpose. RAID Level 6 requires a minimum of 4 drives to implement

Characteristics & Advantages

• RAID 6 is essentially an extension of RAID level 5 which allows for additional fault tolerance by using a second independent distributed parity scheme (dual parity)
• Data is striped on a block level across a set of drives, just like in RAID 5, and a second set of parity is calculated and written across all the drives; RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous drive failures
• RAID 6 protects against multiple bad block failures while non-degraded
• RAID 6 prodects against a single bad block failure while operating in a degraded mode
• Perfect solution for mission critical applications

Disadvantages

• More complex controller design
• Controller overhead to compute parity addresses is extremely high
• Write performance can be brought on par with RAID Level 5 by using a custom ASIC for computing Reed-Solomon parity
• Requires N+2 drives to implement because of dual parity scheme

Recommended Applications

File and Application servers

Database servers

Web and E-mail servers

Intranet servers

Excellent fault-tolerance with the lowest overhead

RAID Level 10: Very High Reliability combined with High Performance

RAID Level 10 requires a minimum of 4 drives to implement

Characteristics & Advantages

• RAID 10 is implemented as a striped array whose segments are RAID 1 arrays
• RAID 10 has the same fault tolerance as RAID level 1
• RAID 10 has the same overhead for fault-tolerance as mirroring alone
• High I/O rates are achieved by striping RAID 1 segments
• Under certain circumstances, RAID 10 array can sustain multiple simultaneous drive failures
• Excellent solution for sites that would have otherwise gone with RAID 1 but need some additional performance boost

Disadvantages

• Very expensive / High overhead
• All drives must move in parallel to proper track lowering sustained performance
• Very limited scalability at a very high inherent cost

Recommended Applications

• Database server requiring high performance and fault tolerance

RAID Level 50: High I/O Rates & Data Transfer Performance

RAID Level 50 requires a minimum of 6 drives to implement RAID 50 should have been called “RAID 03″ because it was implemented as a striped (RAID level 0) array whose segments were RAID 3 arrays (during mid-90s) Most current RAID 50 implementation is illustrated above RAID 50 is more fault tolerant than RAID 5 but has twice the parity overhead High data transfer rates are achieved thanks to its RAID 5 array segments High I/O rates for small requests are achieved thanks to its RAID 0 striping Maybe a good solution for sites who would have otherwise gone with RAID 5 but need some additional performance boost Very expensive to implement All disk spindles must be synchronized, which limits the choice of drives Failure of two drives in one of the RAID 5 segments renders the whole array unusable

RAID Level 0+1: High Data Transfer Performance

RAID Level 0+1 requires a minimum of 4 drives to implement

Characteristics & Advantages

• RAID 0+1 is implemented as a mirrored array whose segments are RAID 0 arrays
• RAID 0+1 has the same fault tolerance as RAID level 5
• RAID 0+1 has the same overhead for fault-tolerance as mirroring alone
• High I/O rates are achieved thanks to multiple stripe segments
• Excellent solution for sites that need high performance but are not concerned with achieving maximum reliability

RAID 0+1 is NOT to be confused with RAID 10. A single drive failure will cause the whole array to become, in essence, a RAID Level 0 array

Disadvantages

Very expensive / High overhead All drives must move in parallel to proper track lowering sustained performance Very limited scalability at a very high inherent cost

Recommended Applications

Imaging applications

General fileserver

 Source Tom’s hardware

Sometimes you want people to know who you are, while other times you do not. By default on the Internet, with each and every connection you make you broadcast your location with your public IP address—unless you take steps to protect your identity. That IP address can be used to track you and your activities; it can also be used to locate where you are geographically. The Internet is not anonymous. There are, however, a number of different solutions with which you can hide your real IP address and, in effect, have an “anonymous” Web experience. Fundamentally, the mechanism by which the anonymous Web experience is achieved is by way of some form of proxy. That is either a proxy client that is installed locally on your own network or PC or one that is available as a browser-based service online. Traffic from your PC is redirected through the proxy making it look to the outside world as if the proxy (which has a different IP address) is where the traffic originated from. In this review, we look at some of the different options, including Anonymyizer, NetConceal and Vidalia (Tor), as well as a number of online services such as Anonymouse and Megaproxy. We’ll evaluate what works well and what does not to help make you anonymous online.

2. Anonymizer

Anonymizer

The Anonymizer software product is one of the best-known Web solutions in this space. Over the years, it has morphed from a simple online-only service that lets users type in an address they wanted to visit anonymously to a full desktop suite. The full Anonymizer suite includes anonymous Web surfing, spyware scanning, anonymous email addresses and spam protection. For the purposes of this review, we’re primarily concerned with just the anonymous Web surfing application called Anonymous Surfing. Installing Anonymizer’s anonymous Web surfing application is relatively easy and painless. Anonymizer has a free seven-day trial, which installed without incident for our evaluation and was up and running within minutes without the need to reboot the PC. The trial also includes Anonymizer Spyware scanner, digital shredder cookie/cache cleaner and the Nyms anonymous email service. You don’t need to actually run all of them, and in our test, we actually just installed the Web surfing component which provides a great deal of functionality on its own. Anonymizer: Anonymous Surfing main dashboard Anonymizer : Anonymous Surfing main dashboard A main feature of the anonymous surfing application is the ability to mask your IP address. Anonymizer really makes this easy to control with a simple On/Off button setup. They also clearly show you what your actual IP address is and then show what your “anonymized” IP address is without having to activate the service. You don’t get a choice of what the new IP address will be with Anonymizer; it’s changed automatically by Anonymizer every 24 hours. You also cannot choose geography either, so your new IP will always be located in the United States. Beyond just providing you with a different IP address, Anonymizer also offers a check box where you can filter the sites you browse for malicious content. There is also an option to have the connection SSL encrypted, which provides another degree of security as it encrypts your traffic between your location and the proxy server. By virtue of having the traffic SSL encrypted, Anonymizer also claims that it offers Wi-Fi security since all your traffic is encrypted and not open for prying eyes to look at. As an added bonus, all the sites that you visit while surfing when Anonymizer is activated are also validated against phishing (fake address sites) and pharming (where the DNS is pointing you to the wrong site) as well. The phishing, pharming, SSL protection and malicious Website protection service are all part of the core Anonymous Web Surfing application, so no need to buy anything else to get those features. While it’s great that Anonymizer clearly communicates the address of what it calls your “anonymous” IP address, it’s always a good idea to check and see if that’s how others actually see it. Among the most basic ways of testing Anonymizer’s IP address claims is by visiting a site like WhatIsMyIp.com or Ipexposed.com where your public IP address is displayed. With Anonymizer there was no incident; the IP address the program claimed it was providing was the one that others saw too. Not all proxies are anonymous though, and there are a number of ways by which a site can detect whether or not you are using a proxy (and then potentially block you). As such, it’s also a good idea to use a form of a ProxyJudge script that tests the information sent from your local PC in the HTTP header information in order to validate whether or not you actually are anonymous (or just seen to be using a proxy). For this review we opted for a free online ProxyJudge script at: http://www.proxyserverprivacy.com/adv-free-proxy-detector.shtml to validate the various services. In the case of Anonymizer, the result was that no proxy was detected at all - which is result you want to see. It means that from the outside world’s point of view you are who you say you are and there is no obvious reason to suspect otherwise. Now to be fair, there are other mechanisms by which your real IP could perhaps be discovered including a rogue JavaScript or flash file. Anonymizer does not offer the option of blocking those types of files in the dashboard, but as a user, it’s something that you might want to consider doing on your own in your own local browser. The other issue to consider is speed. In limited testing we found that using Anonymizer resulted in a bandwidth speed decrease ranging from 25% to 50% (using third-party speed test tools at Broadbandreports.com and Whatismyip.com). In general, most of the anonymous-IP services we tested had some performance hit over running a naked (“non-anonymized”) connection.

3. NetConceal Anonymity Security Shield

NetConceal Anonymity Security Shield

NetConceal Anonymity Security Shield is an interesting offering providing users with the ability to choose their proxy from an automatically generated list. In addition to using the proxy for Web traffic, NetConceal also offers the promise of being able to use the proxy for other IP services as well, such as instant messaging or email. NetConceal setup Setup for NetConceal You can also specify which geography you want the proxy to be from as well as specifying SSL-only proxies. NetConceal options NetConceal options for selecting type and location of the proxy. Once the proxy has been selected, NetConceal bounces you over to a new screen that is supposed to validate what in fact you’re running with a different IP address. NetConceal fake address The NetConceal fake address page Unfortunately not all of the proxies in the NetConceal list were as reliable as we would have liked. We experienced intermittent connection difficulties with various proxies where sometimes the proxy worked and passed traffic reliably and sometimes it didn’t. The NetConceal start window in the browser warns that you need to stay in the same window to be anonymous. But once you start surfing, there is no indication either in the task bar, navigation bar or otherwise that you’re surfing with a different proxy. Additionally, not all sites were accessible, including the third-party sites we attempted to visit to verify the proxy and the IP address. Once launched, there is no simple dashboard to just switch proxies or to switch a proxy off (other than closing the window that first started browsing with). The ability to practically anonymously surf the Web is a great idea, but as was the case with the browser, proxy connections for non-browser internet activities were not always 100% reliable.

4. Vidalia (Tor/Privoxy)

Vidalia

While there are many different public open proxies on the Internet today, the Tor onion router network is specifically about providing users with a degree of privacy and anonymity. The Tor project claims that hundreds of thousand of people use the Tor network to provide privacy. Though Tor is popular, by itself it’s not quite as easy to take advantage of as it could be and that’s where Vidalia comes in. Vidalia is a packaged application that includes Tor, the Privoxy local proxy as well as the Vidalia GUI for managing the Tor experience. With the one Vidalia download, you end up with a local Privoxy proxy loaded on your local PC with an instance of Tor to connect through for privacy. Vidalia control panel The Vidalia control panel The Vidalia control panel shows you the status of your Tor connection, lets you start and stop it and provides an easy way to change proxies with the Use a New Identity button. Vidalia also offers a bandwidth graph so you can see exactly how much traffic you’ve sent through Tor. If you’re curious to see how big the Tor network is and how traffic flows, there is also an option to view the network Vidalia Tor Network Map Vidalia: Tor Network Map showing connection activity To get Vidalia to work with your Internet applications, there are a few different approaches. Since the Privoxy part of Vidalia is a local proxy, you can simply set any browser you may use to connect through the local proxy at the address and port what you specify in the Vidalia settings. For Mozilla Firefox users, taking advantage of Tor with Vidalia is even easier with a simple add-on called TorButton. With TorButton, there is a small indicator at the bottom of the browser display that you click on or off in order to activate an anonymous browsing experience. While Vidalia makes Tor easy to use, there are still a few things the Vidalia control panel does not easily enable. For example, there is no easy way to specify or enable an SSL proxy. Also, there is no easy way to ensure that the proxy you select is in fact an anonymous proxy. Using the free online ProxyJudge script at: http://www.proxyserverprivacy.com/adv-free-proxy-detector.shtml, we had proxies that were identified as anonymous as well as those that could be identified as being proxies—it all depended on which Tor server we were connected to. The same issue goes for speed with Vidalia. While some Tor servers didn’t seem to impact our bandwidth by more than 25%, some servers were somewhat slower (several resulted in an 80% bandwidth or greater speed reduction). Vidalia is, however, free and it is open source. You can also (if you’re so inclined) look at the source code and modify and/or extend it you need to.

5. MegaProxy

MegaProxy

So far the services we’ve looked at have all required a local client download. However, there are also online anonymous proxy services, such as the package MegaProxy offers. MegaProxy has two offerings: One is a free service that provides a basic degree of anonymity and security and the second is a paid service with additional security features (and a cost of $9.99 for three months). For the purposes of this review we evaluated the free option, since MegaProxy (unlike Anonymizer) does not offer a free trial of its SSL enabled service. That said, the free MegaProxy is no slouch either and works reasonably well. MegaProxy configuration preferences MegaProxy : Configuration preferences with the locked areas as the premium paid features. What MegaProxy provides is a new toolbar that shows up in your main browser window through which you can surf anonymously. In addition to providing a new IP address, MegaProxy also offers users the option of hiding what browser and operating system you may use (which can be tracked, too). It also hides the HTTP referred information that can be used to identify which site you last visited. With the free service, Megaproxy will also encrypt and transform up to 20 web cookies into session-only cookies, which also provides an addition degree of privacy. The free MegaProxy service also performed well in our ProxyJudge test, which was not able to identify that a proxy was in fact being used. While the free MegaProxy service does give you the ability to surf anonymously, there are some restrictions. Among them is that flash files will not filter through the free proxy. Forms and remote logins are restricted. MegaProxy has also put a limit of only being able to view 60 Webpages in a five-hour timeframe. MegaProxy With MegaProxy’s free service, flash files are restricted. For the $9.99 for three months ($40 a year), MegaProxy’s paid service does not have the same usage restrictions. On the privacy side, it provides SSL encryption as well as a neat anti-caching feature, which prevents the browser from storing temporary files.

6. Anonymouse.org

Anonymouse.org

Anonymouse.org is also an online browser-based anonymous-IP service. As is the case with Megaproxy, there is a free service and then there is a paid service. The free anonymouse.org service is ad supported and does not provide SSL encryption. The paid service runs $38 dollars a year and offers SSL as well as some additional cookie handling feature to further ensure privacy. Anonymouse.org Surfing anonymously with anonymouse.org The free version of Anonymouse also had difficulties handling flash files and it does not offer any options for changing the proxy you’re connected to. Additionally, the proxy used by anonymouse.org in the online ProxyJudge test was easily revealed.

7. Product Comparison Matrix

Product	Anonymizer	NetConceal	Vidalia	MegaProxy	Anonymouse

8. Conclusions

Conclusions

Hiding your IP or making it appear to be something other than what it actually is really isn’t a terribly difficult chore. In addition to the tools and services we’ve reviewed in this article, a simple search for “open proxy” in your favorite search engine will yield many more options, as well as lists of open proxies you can use. When surfing the Web with the major browsers, it’s a trivial matter to set the browser to use a proxy instead of connecting directly to the Internet. The problem comes from finding reliable proxies that will work consistently. In the case of Anonymizer, the anonymous-IP service is easy to setup and use, providing a clear picture of what is going on. The built in phishing/pharming/malicious file filter is also a major added bonus. Being limited to just one IP address per day that is limited to the United States, could, however, be a sticking point for some. Anonymizer also does not have an online interface at this point, so it’s limited to just your local PC installation. The Anonymizer Anonymous surfing product is only $29.99 a year, though, which among the paid services is a good deal. NetConceal provides more choices when it comes to proxy selection, but it pales in comparison to Anonymizer’s easy to use management interface. As a paid product, though, NetConceal is only $24.95 and there are no yearly subscription fees. Vidalia’s packaging of the Tor network is a superior choice compared to NetConceal, and with Vidalia’s cost being zero, it’s also an even better deal. The ability to connect into a global network of proxies with Tor is a very good thing, and while not all of the Tor proxies are of the same quality, most work well. On the online proxy side, Anonymouse.org and Megaproxy are similar, while the fact that Megaproxy’s proxy was not reported as a proxy is a huge bonus and one that likely gives it an edge. Then again on the free side of the equation with anonymouse.org, you’re not limited to just 60 sites in five hours - which is a strong negative for the free Megaproxy service. Both Megaproxy and anonymouse.org have paid services that improve speed and performance while providing additional privacy and security measures. Anonymouse.org is $38 a year while the paid Megaproxy service is almost the same at about $40 a year (listed pricing is $9.99 for 90 days). If you need an online service that you want for free, Anonymouse is the way to go. If you’re willing to pay, Megaproxy might have an edge thanks to its improved anti-caching features. If you don’t mind just having a U.S. IP address, then Anonymizer is a solid service. If you’re looking for something more, then Vidalia is a great place to start. It’s important to note that none of these services can entirely protect your IP and your identity but they all will move you in the right privacy direction. Happy (anonymous) surfing!